1. Field of the Invention
This invention relates to a catalyst, a method of making the same and catalytic processes for using the same, more specifically to low temperature selective oxidative dehydrogenation of ethane (or mixture of ethane and ethylene) to acetic acid. The invention also relates to single stage catalytic processes using the novel catalyst featuring increased ethane conversions and acetic acid yields at particular process conditions wherein the product stream does not contain significant amounts of side products such as ethylene and CO.
2. Description of the Related Art
Several publications are referenced in this application. These references describe the state of the art to which this invention pertains, and are incorporated herein by reference.
Due to environmental law constraints, carbon monoxide is an undesirable by-product from an industrial point of view. Furthermore, the separation of ethylene from ethane has a great impact on the process economics of ethane oxidative dehydrogenation processes, where the desired product is an oxygenated hydrocarbon, such as acetic acid.
Acetic acid is conventionally produced by methanol carboxylation using expensive rhodium catalysts in liquid phase homogeneous reactions, which require complicated procedures for the recovery of the catalyst and isolation of the products. More recently, very expensive raw materials for converting ethylene to acetic acid with the production of acetaldehyde as a by-product has been reported.
European Patent Publication EP 02 94 845 discloses a process for the higher selective production of acetic acid by the oxidation of ethane with oxygen in contact with a physical mixture of two catalysts consisting of (A) a catalyst for oxydehydrogenation of ethane to ethylene and (B) a catalyst for hydration/oxidation of ethylene. The ethane oxydehydrogenation catalyst is represented by the formula Mo.sub.x V.sub.y Z.sub.z, wherein Z can be one or more of the metals Nb, Sb, Ta, Ca, Sr, Ti, W, Li, Na, Be, Mg, Zn, Cd, Hg, Sc, Fe and Ni. The catalyst for the hydration/oxidation of ethylene is selected from a molecular sieve catalyst, a palladium-containing oxide catalyst, tungsten-phosphorus oxides, or tin molybdenum containing oxide catalysts. European Patent Publication EP 02 94 845 employs the catalyst system prepared by a physical mixture of the two types of catalysts.
The use of molybdenum and vanadium containing catalyst systems for low temperature oxydehydrogenation of ethane to ethylene was reported by E. M. Thorsteinson et al., Journal of Catalysts, vol. 52, pp. 116-132 (1978). This paper discloses mixed oxide catalysts containing molybdenum and vanadium together with another transition metal oxide, such as Ti, Cr, Mn, Fe, Co, Ni, Nb, Ta, or Ce. The catalysts are active at temperatures as low as 200.degree. C. for the oxydehydrogenation of ethane to ethylene. Some acetic acid is produced as a by-product.
Several U.S. Patent (U.S. Pat. Nos. 4,250,346, 4,524,236, 4,568,790, 4,596,787 and 4,899,003) have been granted on low temperature oxydehydrogenation of ethane to ethylene. U.S. Pat. No. 4,250,346 relates to the use of catalysts of the formula Mo.sub.h V.sub.i Nb.sub.j A.sub.k in which A is Ce, K, P, Ni, and/or U, h is 16, i is 1 to 8, j is 0.2 to 10, and k is 0.1 to 5. U.S. Pat. No. 4,454,236 is directed to the use of a calcined catalyst of the formula Mo.sub.a V.sub.b Nb.sub.c Sb.sub.d X.sub.e.
The above-cited patents make reference to other patents concerned with the production of ethylene from ethane by the oxydehydrogenation process and all make reference to the formation of acetic acid as a by-product.
U.S. Pat. Nos. 4,339,355 and 4,148,757 relate to oxide catalysts containing Mo, Nb, V and a fourth metal selected from Co, Cr, Fe, In, Mn or Y for the oxidation/ammoxidation of unsaturated aliphatic aldehydes to corresponding saturated aliphatic carboxylic acids.
European Patent Publication EP 04 80 594 is directed to the use of an oxide catalyst composition comprising tungsten, vanadium, rhenium and at least one of the alkaline metals for the production of ethylene and acetic acid by oxidation of ethane with a molecular oxygen containing gas. The replacement of tungsten in whole or part by molybdenum carried out in European Patent Publication EP 04 07 091 results in an increase in selectivity to acetic acid at the expense of the selectivity to ethylene.
European Patent Publication EP 05 18 548 relates to a process for the production of acetic acid by ethane oxidation in contact with a solid catalyst having the empirical formula VP.sub.a M.sub.b O.sub.x, where M is one or more optional elements selected from Co, Cu, Re, Nb, W and many other elements, excluding molybdenum, a is 0.5 to 3, b is 0 to 0.1.
European Patent Publication EP 06 27 401 relates to the use of a V.sub.a Ti.sub.b O.sub.x catalyst for the oxidation of ethane to acetic acid. The catalyst composition may comprise additional components from a large list of possible elements.
Furthermore, catalysts containing MoVNb promoted with phosphorus and boron have recently been reported as producing a relatively higher yield of acetic acid as compared to unpromoted catalysts with the production of by-products such as carbon monoxide, carbon dioxide and ethylene. See, U.S. application Ser. No. 08/932,075, filed Sep. 17, 1997, by Karim et al., entitled "Catalysts for the Oxidation of Ethane to Acetic Acid, Processes of Making Same and Processes of Using the Same".
More recently, a catalyst containing niobium, palladium, molybdenum and vanadium is reported for use in an ethane oxidation process. See, U.S. application Ser. No. 08/997,913, filed Dec. 24, 1997, by Karim et al., entitled "Catalysts For Producing Acetic Acid From Ethane Oxidation, Processes of Making Same And Methods of Using Same". From a commercial point of view, niobium is an expensive raw material which can have a great impact on the catalyst cost and consequently on the process economics.
Thus, none of these publications have disclosed or suggested the advantages of the catalysts disclosed in present invention which are commercially cheaper and have higher performance for selective production of acetic acid through single stage partial oxidation process of ethane with reduced or zero production of carbon monoxide and ethylene and higher yield and/or selectivity of acetic acid.